Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Limite del bosco
3 · Marcato
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In sintesi

Precipitation is forecasted Thursday night through Saturday, with snowline initially hovering around 4000ft. Wind slabs will develop on leeward slopes at higher elevations, while the snowpack will saturate with rain at lower elevations. Avoid wind loaded slopes greater than 35 degrees, and in areas with wet snow avoid steep slopes and the runouts beneath them. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2

    Dangerous wind slabs will develop as snowfall amounts increase and wind continues throughout the day on Friday. Avalanches will most likely remain in the new snow deposited in the last 24 hours. We could receive up to a foot or more of snow by midday Friday so you could find slabs several feet deep.  Strong winds from the south will redistribute snow onto leeward slopes and crossload features. Feel for stiffer snow and observe signs of active wind loading to determine where wind slabs are. Cornices have grown very large in recent days, and with more snow loading them they could fail and trigger a large avalanche on the slope beneath.  Avoid wind loaded slopes steeper than 35 degrees during this storm. If you see red flags such as natural avalanches and large cracking be prepared to stay even more conservative with your travel.

    (3/3/2021) Wind loading was actively occurring in the Twin Sisters area on Wednesday 3/3. Photo: Zach McGill

  • Loose Wet

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    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    We could see enough rain at lower elevations that the top few feet of snow will get saturated with water. Due to the amount of rain (possibly totalling an inch by midday Thursday), expect avalanche size to be larger than the recent small wet loose avalanches which occurred on south slopes. Avalanches will occur on all aspects, and possibly larger on northerly slopes which did not get affected by the sun previously. Avalanches up to a couple feet deep will carry larger amounts of mass, which could easily bury you or cause harm if they push you through trees or deeply bury you in a gully. Avoid steep slopes and their runouts where the snow is getting saturated with rain, as loose wet avalanches may occur. 

    Keep an eye out for glide cracks in lower elevation areas where a glide avalanche may occur. This is especially the case in steep mid to lower elevation slopes where the bed surface (ground) is smooth rock or grass, where glide avalanches tend to happen.

    Large wet loose avalanches may occur on Friday.

Avalanche Discussion

This storm will test the snowpack once again after a few days of fair weather where we saw very few large avalanches. There are uncertainties in the top 10+ feet in our snowpack, although in our zone most  avalanches have been limited to new snow instabilities in the last several days. 

Last week there was a widespread natural avalanche cycle that resulted in many very large avalanches (D3+) some of which hit Highway 20 just outside Newhalem. Additional very large avalanches occurred in the southerly portion of the zone, which may have failed on the deeper weak layer from January.  This layer is 200cm - 300cm deep in most areas and it is hard for a human to trigger it. However, a big cornice falling in the right spot could trigger an avalanche on that layer. 

The take-home is that snow and avalanche conditions are variable in the West North zone and throughout the Cascades right now. In general, recent storm snow is stabilizing quickly, but very large natural avalanches along the border of the Stevens and West Central zones continue to keep these old and deep weak layers on our minds in this zone as well. Read the West Central or Stevens Pass Forecasts to learn more about it. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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